1. Field of the Invention
The present invention is directed to an electromagnetic acoustic pressure pulse source, of the type having a membrane which is electrically conductive in at least one region, an acoustic propagation medium disposed on one side of the membrane, and a flat, spiral coil arrangement disposed on an opposite side of the membrane, for driving the membrane to cause the generation of a pressure pulse in the acoustic propagation medium.
2. Description of the Prior Art
Pressure pulse sources are used, for example, for medical purposes in the treatment of stone pathologies (lithotripsy), tumors and bone pathologies (osteorestoration). An electromagnetic shockwave generator is disclosed in European Application 0 259 559 wherein pressure pulses are generated by driving the membrane with a spiral coil arrangement having terminals connected to a high-voltage pulse generator which charges the coil with high-voltage pulses having an amplitude in the kilovolt range, for example, 20 kV. Such high-voltages can be generated, for example, by capacitor discharges. When the spiral coil arrangement is charged with such a high-voltage pulse, it generates a magnetic field extremely quickly. Simultaneously, a current is induced in the membrane, or at least in the electrically conductive region thereof, which is directed oppositely to the current flowing in the coil. The membrane current consequently produces an opposing magnetic field, causing the membrane to be rapidly moved away from the spiral coil arrangement. The pressure pulse initiated in the acoustic propagation medium, which is preferably a liquid such as water, is introduced in a suitable manner into the subject to be charged with the pressure pulses. As necessary, focusing of the pressure pulses may be undertaken before the pressure pulses reach the subject, for example by means of an acoustic lens.
In order to achieve a high efficiency of the energy conversion while avoiding voltage arcing between the spiral coil arrangement and the membrane (or the electrically conductive region thereof), which can reduce the useful life of the pressure pulse source, known pressure pulse sources provide a spacing between the turns of the spiral coil arrangement and the membrane which is greater in those regions of large potential differences between the turns of the spiral coil arrangement and the membrane, as compared to regions having a smaller potential difference. This is achieved in known structures by arranging the turns of the spiral coil on a seating surface consisting of an insulating material which is shaped so that the aforementioned spacing results between the turns of the spiral coil and the membrane. Thus even in the case of standard, planar membranes, a planar seating surface cannot be used. The presence of this uneven seating surface complicates both the manufacture of the seating surface and the winding of the spiral coil arrangement thereby resulting in substantial production-associated outlay and increased manufacturing time and costs.